Large generators have stator cores, which usually comprise many axially thin annular laminations that are assembled together and compressed to form a cylindrical stator core supported in a frame. Known magnetic cores of some types of such generator stators require the installation of longitudinal bolts to maintain the tightness of the core components. These bolts are arranged parallel to the stator axis and are distributed over the outer and inner circumference of the magnetic core. The bolts are called “through bolts” and extend axially through bores provided in the stator core lamination. The through bolts are provided with nuts on both axial ends of the through bolts which are torqued or hydraulically tensioned to hold the core support system in assembled position. Further, the through bolts are generally wrapped with dielectric insulation.
The relaxation of these through bolts or defects of the lamination will affect the integrity of the stacked core. If the tension of the through bolts is lost, re-tightening of the bolts could be insufficient. In such a case the replacement of the through bolts is required. Other cases where replacement of the through bolts becomes necessary is the retrofitting of the generator.
However, often the generator is located in a space below the normal floor level. Thus, difficulties often arise due to the lack of clearance between the end of the stator core and the wall of the foundation or floor level of the building. Such an absence of clearance prevents the axial alignment for insertion of the through bolts into the bores of the stator core. To overcome the lack of clearance, one solution suggests to lift the frame together with the core to obtain the clearance necessary to introduce the through bolts.
Alternatively U.S. Pat. No. 4,845,836 suggests using a special apparatus for feeding a through bolt through the bores of a stator core while initially feeding the same towards the end of the bore along a line forming an acute angle with the axis of the bore. The apparatus uses several rollers to deflect the through bolts from the acute angle at which they are fed and coaxially align them with the axis of the bore. The apparatus according to U.S. Pat. No. 4,845,836 is relatively complicated and the method is very troublesome to use, especially if all of the through bolts need to be replaced.